does anyone know if military prison is like civilian prison, in which you could be released early for a variety of factors including overcrowding, good behavior

does anyone know if military prison is like civilian prison, in which you could be released early for a variety of factors including overcrowding, good behavior, appeals, parole, just plain ambiguity of sentencing, etc? from what i read in the media it seems as though civilian sentences for non-capital crimes are basically flexible.... but i'm no expert.